Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) with a presumed autoimmune etiology. Experimental autoimmune encephalomyelitis (EAE) is frequently used as an animal model of MS. EAE can be induced in susceptible mouse strains by injection of CNS proteins or peptides together with adjuvants. Most studies have indicated that myelin-specific T helper type 1 (Th1) cells secreting IFN-gamma and TNF-alpha mediate EAE and MS. whereas myelin-specific Th2 cells producing IL-4 and IL-10 play a regulatory role. Studies with animal models have demonstrated that modulation of immune responses from a Th1-dominant to a Th2-dominant response can effectively protect mice against EAE. Natural killer T (NKT) cells are a subset of T lymphocytes that co-express surface markers characteristic of conventional T cells and NK cells. The invariant Valpha14 T cell receptor of NKT cells is specific for glycolipid antigens bound with the non-polymorphic MHC class I-like protein CD1d. While the precise immunological function of NKT cells remains unknown, these cells have been implicated in protective immune responses against pathogens and tumors, and in the regulation of autoimmune responses. Prior work conducted in the PI's laboratory has shown that ligand-specific activation of NKT cells with the glycolipid alpha-galactosylceramide (alpha-GalCer) polarizes adaptive immune responses for production of Th2 cytokines in mice. These findings suggest that alpha-GalCer can inhibit Th1 -oriented immune responses, providing an alternative way to suppress immune responses that cause pathology in organ-specific autoimmune diseases such as MS. Indeed, our preliminary results have revealed that alpha-GalCer prevents the induction of EAE in susceptible mice. Based on our published findings and preliminary results, the central hypothesis of this grant application is that NKT cells represent a novel target cell type for immunomodulation of EAE and MS. We will test this hypothesis in four Specific Aims. Aim 1 will investigate the mechanism by which ligand-activated CD1d-resticted NKT cells modulate EAE. Aim 2 will evaluate whether disease protection conferred by a-GalCer is an active suppressive process. Aim 3 will determine the potential synergy of alpha-GalCer with other immunomodulatory reagents for prevention of EAE disease. Aim 4 will evaluate the ability of alpha-Ga1Cer analogues to protect mice against EAE. These studies will provide a better understanding of the immunological functions of NKT cells and the mechanisms that mediate autoimmunity. At the completion of this project, we expect to have identified a set of reagents (NKT cell ligands, cytokines, blocking antibodies) that can be utilized to specifically activate or inhibit different effector functions of NKT cells. These reagents will permit the selective activation of distinct adaptive immune responses in vivo, which could be exploited for therapeutic intervention in MS and other human autoimmune diseases.